1. Field of the Invention
The present invention relates to an electric double layer capacitor and a battery. More specifically, the present invention relates to an electric double layer capacitor and a battery in which a cell is covered by an outer package in a decompression state.
2. Description of Related Art
Electric double layer capacitors have been conventionally used in practice and the structural characteristics thereof have recently been utilized to further decrease their sizes and increase their capacities. For instance, considerations have been made for new uses of electric double layer capacitors, such as a driving power source for a cell motor of a vehicle in combination with a lead battery or an auxiliary power source in combination with a solar battery.
Examples of the structure of electric double layer capacitors include the one shown in FIGS. 7 and 8.
The electric double layer capacitor shown in FIG. 7 includes a basic cell 55 which is constituted by a separator 51 of porous sheet type, a pair of polarized electrodes 52 and 52 of plate shape, a pair of collectors 53 and 53 of sheet shape, and gaskets 54 of frame shape. The pair of polarized electrodes 52 is disposed so as to sandwich and make contact with the separator 51 from both sides. The pair of collectors 53 is disposed so as to sandwich the polarized electrodes 52. That is, each of the pair of collectors 53 makes contact with the surface of the polarized electrodes 52 which is opposite the surface making contact with the separator 51. The gaskets 54 are disposed between the pair of collectors 53 so as to make contact with end surfaces of the polarized electrodes 52. The basic cell 55 contains an electrolyte sealed inside thereof.
In the electric double layer capacitor, a plurality of the above-mentioned basic cells 55 is laminated to form a multi-layered cell 56 shown in FIG. 8. In FIG. 8, an electrode plate 57 to which a lead terminal is connected is closely attached to the collectors 53 located at the outermost side in the laminated direction of the multi-layered cell 56, and the whole is covered by an outer package 58 in a decompression state (i.e., vacuum packed).
Since the electric double layer capacitor is covered by the outer package 58 in a decompression state, a compressive force is always applied to the capacitor from the outside due to atmospheric pressure. As a result, the degree of contact between the basic cells 55 and 55, and between the basic cell 55 and the electrode plate 57 having the lead terminal is enhanced to decrease the equivalent series resistance (ESR). Accordingly, the performance of the capacitor may be further improved and stabilized.
The need for an electric double layer capacitor having an improved performance has recently been increasing and a further reduction of the ESR thereof is awaited. It has been discovered that if, for instance, a conductive film in which carbon is dispersed in an olefin resin is used for the collector 53 instead of a conventional conductive rubber in which carbon is dispersed in butyl rubber, the ESR of the collector 53 may be further reduced.
However, some of the above-mentioned conductive films have gas permeability coefficients higher than those of conventional ones, and electrolytes contained in the basic cells 55 may be gasified and leaked out from an interface 59 between the collectors 53 and the electrode plate 57 of the basic cells 55 which are located at the outermost side of the multi-layered cell 56 in some cases. If a gas were to leak out from the basic cell 55, the decompression state in the outer package 58 would no longer be maintained and the degree of contact between the basic cells 55 and 55, and between the basic cell 55 and the electrode plate 57 having a lead terminal would decrease. If the degree of contact were to decrease, the ESR thereof increases and the performance as a capacitor deteriorates and becomes unstable. This kind of problem is especially conspicuous under a high temperature atmosphere.
The present invention takes into consideration the above-mentioned circumstances, with an object of providing an electric double layer capacitor and a battery, which uses a material having high gas permeability constant for a collector in order to decrease the ESR, yet capable of preventing the increase of ESR due to a gas leak and, hence, electric performance thereof may be stabilized even under a high temperature atmosphere.
The present invention provides an electric double layer capacitor, including: at least one basic cell containing an electrolyte inside thereof, the basic cell may be laminated in its thickness direction to form a layered cell, including: a separator; a pair of polarized electrodes disposed so as to sandwich and make contact with the separator; a pair of collectors disposed so as to sandwich the polarized electrodes, each one of the pair of collectors making contact with the surface of one of the pair of polarized electrodes which opposes the surface making contact with the separator; and a gasket disposed between the pair of collectors so as to surround the pair of polarized electrodes; an electrode plate including an electrode body and a lead terminal extending from the electrode plate body, the electrode plate body being attached to the outer surface of each one of the collectors located at the outermost side in a laminated direction of the basic cell; an outer package which covers the basic cell and the electrode plate in a decompression state; and a sealing material having a higher gas barrier property than the collectors, the sealing material being disposed so as to seal an interface between each one of the collectors, which are located at the outermost side in a laminated direction of the basic cell, and the electrode plate body in the outer package.
According to the above electric double layer capacitor, since the sealing material having a higher gas barrier property than the collectors is disposed so as to seal an interface between each one of the collectors, which are located at the outermost side in a laminated direction of the basic cell, and the electrode plate body in the outer package, it becomes possible to prevent the electrolyte from being gasified and leaking out from the interface between the collector and the electrode plate body.
Accordingly, even if the collector were formed by using a material having a high gas permeability constant in order to lower the ESR thereof, the decompression state inside the outer package might be suitably maintained. Thus, it becomes possible to prevent an increase in the ESR due to a gas leak, and the electrical properties of the capacitor may be stabilized even if the capacitor were to be used under a high temperature atmosphere.
In accordance with another aspect of the invention, the gas permeability coefficient of each one of the collectors is at least 1xc3x9710xe2x88x9212[m3/(m2xc2x7sxc2x7Pa)].
According to the above electric double layer capacitor, since the gas permeability coefficient of a collector becomes 1xc3x9710xe2x88x9212[m3/(m2xc2x7sxc2x7Pa)] or greater, the amount of electrolyte which is gasified and leaked out from an interface between the collector and the electrode plate body to the inside of the outer package becomes too large to be ignored, the effect of preventing a gas leak due to the presence of the above-mentioned sealing material becomes significant.
In yet another aspect of the present invention, the electrode plate body extends in a circumferential direction thereof, and the sealing material is disposed between the extended portion of each one of the electrode bodies so as to surround the basic cell.
According to the above electric double layer capacitor, since the electrode plate body extends in a circumferential direction thereof and the sealing material is disposed between the extended portion of each one of the electrode bodies so as to surround the basic cell, the sealing material is not present between the basic cell and the electrode plate. Accordingly, it becomes possible to prevent a decrease in the degree of contact between the basic cell and the electrode plate due to the presence of the sealing material therebetween.
In yet another aspect of the present invention, the sealing material is disposed between an outer periphery portion of each one of the collectors, which are located at the outermost side in a laminated direction of the basic cell, and the electrode plate body.
According to the above electric double layer capacitor, since the sealing material is disposed between an outer periphery portion of each one of the collectors and the electrode plate body, the shape of the electrode plate body may be designed to be the same as that of the collector and, hence, the size and weight of the electric double layer capacitor may be reduced.
In yet another aspect of the present invention, the electrode plate body is disposed on each one of the collectors, which are located at the outermost side in a laminated direction of the basic cell, so as to be located more inwardly with respect to the outer periphery portion of each one of the collectors, and the sealing material is disposed so as to surround the electrode plate body and cover portions of each one of the collectors not covered by the electrode plate body.
According to the above electric double layer capacitor, since the electrode plate body is disposed on each one of the collectors so as to be located more inwardly with respect to the outer periphery portion of each one of the collectors, and the sealing material is disposed so as to surround the electrode plate body and cover portions of each of the collectors not covered by the electrode plate body, the sealing material is not present between the basic cell and the electrode plate body. Thus, it becomes possible to prevent a decrease in the degree of contact between the basic cell and the electrode plate due to the presence of the sealing material.
The present invention also provides a battery, including: at least one basic cell containing an electrolyte inside thereof, the basic cell may be laminated in its thickness direction to form a layered cell, including: a separator; a pair of polarized electrodes disposed so as to sandwich and make contact with the separator; a pair of collectors disposed so as to sandwich the polarized electrodes, each one of the pair of collectors making contact with the surface of one of the pair of polarized electrodes which opposes the surface making contact with the separator; and a gasket disposed between the pair of collectors so as to surround the pair of polarized electrodes; an electrode plate including an electrode body and a lead terminal extending from the electrode plate body, the electrode plate body being attached to the outer surface of each one of the collectors located at the outermost side in a laminated direction of the basic cell; an outer package which covers the basic cell and the electrode plate in a decompression state; and a sealing material having a higher gas barrier property than the collectors, the sealing material being disposed so as to seal an interface between each one of the collectors, which are located at the outermost side in a laminated direction of the basic cell, and the electrode plate body in the outer package.
According to the above battery, since the sealing material having a higher gas barrier property than the collectors is disposed so as to seal an interface between each one of the collectors, which are located at the outermost side in a laminated direction of the basic cell, and the electrode plate body in the outer package, it becomes possible to prevent the electrolyte from being gasified and leaked out from the interface between the collector and the electrode plate body.
Accordingly, even if the collector is formed by using a material having a high gas permeability constant in order to lower the ESR thereof, the decompression state inside the outer package may be suitably maintained. Thus, it becomes possible to prevent an increase in the ESR due to a gas leak, and the electrical properties of the capacitor may be stabilized even if the capacitor is used under a high temperature atmosphere.
In accordance with another aspect of the invention, the battery has the gas permeability coefficient of each one of the collectors being at least 1xc3x9710xe2x88x9212[m3/(m2xc2x7sxc2x7Pa)].
According to the above battery, since the gas permeability coefficient of a collector becomes 1xc3x9710xe2x88x9212[m3/(m2xc2x7sxc2x7Pa)] or greater, the amount of electrolyte which is gasified and leaked out from an interface between the collector and the electrode plate body to the inside of the outer package becomes too large to be ignored, the effect of preventing a gas leak due to the presence of the above-mentioned sealing material becomes significant.
In yet another aspect of the present invention, the battery has the electrode plate body extends in a circumferential direction thereof, and the sealing material is disposed between the extended portion of each one of the electrode bodies so as to surround the basic cell.
According to the above battery, since the electrode plate body extends in a circumferential direction thereof and the sealing material is disposed between the extended portion of each one of the electrode bodies so as to surround the basic cell, the sealing material is not present between the basic cell and the electrode plate. Accordingly, it becomes possible to prevent a decrease in the degree of contact between the basic cell and the electrode plate due to the presence of the sealing material therebetween.
In yet another aspect of the present invention, the battery has the sealing material disposed between an outer periphery portion of each one of the collectors, which are located at the outermost side in a laminated direction of the basic cell, and the electrode plate body.
According to the above battery, since the sealing material is disposed between an outer periphery portion of each one of the collectors and the electrode plate body, the shape of the electrode plate body may be designed to be the same as that of the collector and, hence, the size and weight of the electric double layer capacitor may be reduced.
In yet another aspect of the present invention, the battery has the electrode plate body disposed on each one of the collectors, which are located at the outermost side in a laminated direction of the basic cell, so as to be located more inwardly with respect to the outer periphery portion of each one of the collectors, and the sealing material is disposed so as to surround the electrode plate body and cover portions of each one of the collectors not covered by the electrode plate body.
According to the above battery, since the electrode plate body is disposed on each one of the collectors so as to be located more inwardly with respect to the outer periphery portion of each one of the collectors, and the sealing material is disposed so as to surround the electrode plate body and cover portions of each of the collectors not covered by the electrode plate body, the sealing material is not present between the basic cell and the electrode plate body. Thus, it becomes possible to prevent a decrease in the degree of contact between the basic cell and the electrode plate due to the presence of the sealing material.